1 bit CPUs don't really make sense anymore because their gate count niche doesn't really exist anymore in discrete chips. The I/O pads around the perimeter of a chip haven't been able to shrink nearly as much as the logic within even on very mature process nodes in the hundreds of nanometers. Basically there's so much die area that for analog reasons can't be shrunk much taken up by simply getting on and off of the die that logic in the few thousand gate count range is basically free.
That's why you see 8 bit MCUs with a useful set of peripherals even in the ~$0.03/ea range where almost all the cost is in testing and packaging the dies.
